Its deadly reputation is no deterrent and its lethal strength is billed as a selling point, including in this message: “fentanyl Powder really potent just got the pure package today! HMU (hit me up) for your needs.”

There were also messages for morphine: “200 mgs morph (morphine),” xanax, “green bars, text or hmu,” ecstasy and marijuana, “Mollys, kush, hmu for deals…..delivery city wide.”

Similar groups worldwide

Stolen goods are also for sale and there’s something for almost everyone: Samsung phones, Gucci purses, brass knuckles and even baby formula.

In most cases, a single click on the Messenger’s profile image sent one directly to that person’s Facebook profile. In some cases, members even posted their cellphone numbers.

“No one worries about being caught,” the participant told CBC News. “I don’t think the police even know about it.”

A Winnipeg police spokesman told CBC News they are aware these sites exist, but confirmed they’ve not made any arrests in relation to them.

In fact, only a handful of authorities throughout the world have cracked down on them.

In May 2016, Colorado authorities, with co-operation from Facebook, shut down a similar group conversation called “Fly Society 420.” In that case, members were mostly high school students, buying and selling hard-core drugs like LSD.

In February 2015, Facebook shut down an Australian group called “Adelaide street pharmacists.”

A Facebook spokesman told CBC News the social networking site investigates any reports of illegal activity. Facebook’s policy, he said, is clear:

“We prohibit the use of Facebook to facilitate or organize criminal activity that causes physical harm to people, businesses or animals, or financial damage to people or businesses. We remove content, disable accounts, and work with law enforcement when we believe there is a genuine risk of physical harm or direct threats to public safety. We also refer information to law enforcement whenever disclosure is we believe it is necessary to prevent harm.”

Illegal Facebook activity tough to bust: researcher

But sniffing out these secret group conversations and shutting them down can be a mammoth task, says Danah Boyd, a researcher of technology and society with Microsoft’s U.S. offices.

It’s “very hard to track all of the illicit uses” that Facebook’s more than 1.7 billion members could be involved in, Boyd said.

Furthermore, the turnover rate of these group Messenger conversations is high. They open, shut down and pop up again under new names regularly. (In fact, within a week of accessing Wpg Drug Mart, the group had renamed itself “204 Drugs.”)

It can therefore be a “frustrating game of whack-a-mole,” Boyd said.

Facebook’s spokesman would not comment on the specific tools used to monitor suspicious activity.

He confirmed that in response to CBC’s story, Facebook’s Messenger team is now investigating the chat groups.